Phoneme (noun) (linguistics)
any of a small set of units, usually about 20 to 60 in number, and different for each language, considered to be the basic distinctive units of speech sound by which morphemes, words, and sentences are represented. They are arrived at for any given language by determining which differences in sound function to indicate a difference in meaning, so that in English the difference in sound and meaning between pit and bit is taken to indicate the existence of different labial phonemes, while the difference in sound between the unaspirated p of spun and the aspirated p of pun, since it is never the only distinguishing feature between two different words, is not taken as ground for setting up two different p phonemes in English.
First recorded in 1890–95; from French phonème, from Greek phṓnēma “sound,” equivalent to phōnē-, verbal stem of phōneîn “to make a sound” (derivative of phonḗ “sound, voice”) + -ma noun suffix denoting result of action
“There is also a phoneme of stress which has a contrastive function..”